red90toyota

This may be covered somewhere else but during my online searches I could not find anyone else that had this same problem with their tachometer.

For reference all this is on a 1990 toyota truck 4cyl 5speed

Here is the story, About 10 years ago I decided to swap my standard gauge cluster with an sr5 model that had the tachometer, oil pressure gauge, battery gauge and all that good stuff. I basically just plugged it in and most everything worked right off the bat. The only thing I never got to work correctly was the oil gauge, which I now know that the gauge gets burned up if you plug it in with the wrong oil sensor on your motor. I was quite happy with this new cluster even though my oil gauge never worked. Anyway, about 5 years ago the tachometer started acting up. It was all or nothing, sometimes it would work fine, sometimes not at all, sometimes it would jump on and off. I never got around to doing anything about it but then my truck was badly wrecked, You can check out my rebuild thread if you want. I had the entire truck apart, I am putting it back together and I am determined to have everything working properly when it goes back on the road. I had read about some common problems, the tach going bad, the igniter or coil having problems or screws coming loose on the back of the cluster. none of these fixes worked for my problem. I decided to start reading the service manual to get some inspiration. The first thing that I noticed was that during a tune up if you do not have a tach in the dash the service manual instructs you to hook up a test tach to the negative lug on the coil, or to a little connection right next to the fuse box under the hood (it is covered by a little rubber cap). This led me to believe that in some way the tach on the dash also gets is signal from there. The wiring diagram shows that the tach in the cluster is connected to the igniter which is right above the coil and there are wires connecting them. I then looked carefully at the back of the cluster. You can easily trace where the wires go. I found the one that I believed to be the signal wire for the tachometer. Then I checked for continuity between this wire and all the wires in the plug going to my igniter, I got nothing. Then I checked continuity from the negative lug on the coil to the wires coming out of the igniter, I found one that matched, I suspect this is the one that sends the signal to the tach. I could not get any continuity between the wires going to the igniter from the wiring harness and the service connection by the fuse box. The wiring diagrams also show that the wire for the tach signal also goes to the a/c amplifier. I got continuity between the wire to the cluster and the a/c amplifier, and from the a/c amplifier to the service connection by the fuse box. I could not get continuity from the a/c amplifier to any of the wires going to the igniter. So I was pretty sure I had a bad wire somewhere unless I had missed something. I ran a temporary wire from the negative lug on the coil to the connection on the cluster and the tach came to life! I then ran a permanent wire from the negative lug on the coil and spliced it into the signal wire for the cluster. This way I just replaced the bad wire instead of having to find the bad spot. Now the tach seems to work just fine and there is continuity from the a/c amplifier, the test port, the cluster and the negative coil lug so I believe everything should be working properly now. I'm not sure if this would have caused problems with the a/c amplifier because I am just now adding a/c to my truck, but I may have avoided some problems there at the same time. my truck is not drivable at this time, put the tach seems to be working when starting the truck and revving it up so I am
now convinced the problem is solved. here are some pics




Here I am pointing at the negative coil lug. I ran my new wire from here and spliced it into the wire right behind my cluster


my test probe is pointing at the pin on the igniter plug that had continuity with the negative lug on the coil. I believe this is where the tach signal comes out of the igniter



here my test probe points to the pin for the tach signal wire (this plug goes into the back of the cluster)


here the manual shows that the tach is connected to the igniter



this picture is a little cut off but it shows the signal coming from the igniter to the a/c amplifier to the tach on the cluster



here it shows that the wire goes from the igniter to the service connection , a/c amplifier, and tach



this is where I spliced in my new wire. the black one coming out of the plug is original, then you can see my red connector with my new green wire and other half of the black one coming out the other side.


here are all my clusters, my original in front, the one I’m using and another one I had to switch the oil gauge out of due to my burning up the first oil gauge


I have no Idea why my wire went bad. In my limited experience, problems with wires are usually related to corroded connections or due to abrasion from the wires not having enough protection from moving parts. I have checked out all the connections that I know of for this wire and they seem to be in good shape. The wire from the igniter goes up to the firewall, then onto the motor. the wiring harness then comes off the motor on the passenger side inner fender. The problem must be between the igniter and the other side of the motor because I could not get continuity from the igniter to the service connection near where the wiring harness comes off of the motor. I am honestly pretty surprised that this was a problem because it looks like Toyota bundled that harness up pretty tight. Also, I know that I mentioned it at the beginning but all of this was on a 1990 truck. I'm sure they moved things around and changed things over the years and due to different options on the trucks so I highly suggest reading your wiring diagrams before you splice the same wires as I did, but it worked for me.

ZUK

iTrader: (1)

Pretty good trouble shooting you did there, Red90

red90toyota

Thanks!